Run 8 solving threads in parallel

Makefile

@@ -22,12 +22,16 @@ CFLAGS += -D_XOPEN_SOURCE=700
 CFLAGS += -march=native
 CFLAGS += -static
 
+LDFLAGS += -lpthread
+
 # For profiling
 # CFLAGS += -pg
 
 SRC = main.c sud.c solve.c
 OBJ = $(SRC:.c=.o)
 
+default: sudoku eval
+
 sudoku: $(OBJ)
 	$(CC) $(CFLAGS) $(LDFLAGS) $(OBJ) -o $@
 
@@ -55,4 +59,4 @@ run: sudoku eval puzzles solns results
 	time ./sudoku
 	./eval
 
-.PHONY: clean run
+.PHONY: default clean run